Magneto-thermal properties and slow magnetic relaxation in Mn(II)Ln(III) complexes: Influence of magnetic coupling on the magneto-caloric effect
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Date
2022-08-05Author
Oyarzabal Epelde, Itziar
Zabala Lekuona, Andoni
Mota Ávila, Antonio José
Palacios, María A.
Rodríguez Diéguez, Antonio
Lorusso, Giulia
Evangelisti, Marco
Rodríguez-Esteban, Corina
Brechin, Euan K.
Colacio Rodríguez, Enrique Emilio
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Dalton Transactions 51(34) : 12954-12967 (2022)
Abstract
A family of Mn(II)Ln(III) dinuclear and tetranuclear complexes (Ln = Gd and Dy) has been prepared from the
compartmental ligands N,N’-dimethyl-N,N’-bis(2-hydroxy-3-formyl-5-bromobenzyl)ethylenediamine
(H2L1
) and N,N’,N’’-trimethyl-N,N’’-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine (H2L2
).
The Mn(II)Gd(III) complexes exhibit antiferromagnetic interactions between Mn(II) and Gd(III) ions in most
cases, which are supported by Density Functional Theory (DFT) calculations. Experimental magnetostructural correlations carried out for the reported complexes and other related complexes found in bibliography show that the highest ferromagnetic coupling constants are observed in di-μ-phenoxido bridged
complexes, which is due to the planarity of the Mn–(μ-O)2–Gd bridging fragment and to the high Mn–
O–Gd angles. The effect of these angles has been studied by DFT calculations performed on a di-μ-phenoxido doubly bridged model. The magneto-thermal properties of the Mn(II)Gd(III) based complexes have
also been measured, concluding that the magnitude of the Magneto-Caloric Effect (MCE) is due to the
strength rather than to the nature of the magnetic coupling. Moreover, when two Mn(II)Gd(III) dinuclear
units are connected by two carbonato-bridging ligands the MCE is enhanced, obtaining a maximum magnetic entropy change of 36.4 Jkg−1 K−1 at ΔB = 7 T and T = 2.2 K. On the other hand, one of the dinuclear
Mn(II)Dy(III) complexes displays Single-Molecule Magnet (SMM) behaviour with an energy barrier of 14.8 K
under an applied external field of 1000 Oe.